In commerce and industry today, the useful life of corrodible items may be extended and/or preserved by providing corrosion inhibitors which protect the corrodible item from the adverse effects of its ambient environment. Corrosion inhibitors, particularly vapor phase corrosion inhibitors, have been found useful in protecting certain corrodible items against reaction with elements or compounds which may be found within their environment, and thereby losing their effectiveness, reducing their useful life, or otherwise diminishing their value. Such protection is typically needed during times of packaging, handling, shipment, or during end use. Elements or compounds which are normally of primary concern are gases such as oxygen, water vapor, sulfides, carbon dioxide, and the like. The vapor phase corrosion inhibitor-desiccant formulations of the present invention find particular application in the preparation of packaging material, particularly through in-situ extrusion of the material with such films, with the films thereafter being utilized to form an envelope or other enclosure about the article being protected. These films may also be employed as a member of a multi-layer laminate including a metallized film having good tear resistant properties such as stress-oriented polyethylene terephthalate containing a vapor deposited film or layer of metallic aluminum on a surface thereof. Such films are commercially available and are commonly designated as "aluminized" films.
Among the common indications of corrosion manifested in useful metallic articles are oxidation, pitting, tarnishing, mottling, or discoloration of the surfaces of these items. These manifestations occur in the articles, particularly when exposed to oxygen and in either gaseous or liquid phase. Additionally, sulfides may present corrosion or tarnishing problems as well. Inasmuch as both oxygen and water, including water vapor, occur normally and are available in nature, it is normally necessary to take precautions against corrosion when packaging metallic items for shipment, or when subjecting such items to normal use. Metals which are frequently found to be susceptible to corrosion under normal atmospheric and ambient conditions are iron, copper, brass, aluminum, silver, and alloys of these metals. The formulations of the present invention are particularly useful in providing protection to both ferrous and non-ferrous metals, including such non-ferrous metals as aluminum, copper and brass. Care must frequently be taken to protect articles fabricated from such metals, even when their surfaces have been treated so as to be provided with sacrificial or aesthetic coatings of zinc or cadmium on their surfaces. Such sacrificial or aesthetic coatings are, of course, in wide use, but restrictions of use of these materials may appear from time to time due to their potential contribution to pollution or the like. Accordingly, means must be provided to find alternate techniques for the protection and/or preservation of metallic articles.
In the past, it has been known to provide a package or other enclosure which includes one or more inhibiting compounds along with the corrodible item or items to be protected. Additionally, articles have been protected by means of utilization of protective coatings in the form of solids, liquids, greases, or pastes, however such coatings tend to be temporary in nature and further present certain disadvantages to normal handling and packaging. Furthermore, removal of such protective coatings may present problems either due to incomplete removal, or the costs of such removal. The composite vapor phase corrosion inhibitor-desiccant materials of the present invention finds application as a solid phase composite which may be co-extruded with the film which is to form the enclosure about the article being protected.
Solid phase and liquid phase compounds have been used in the past to provide a source of vapor phase corrosion inhibitors. These materials typically undergo either evaporation or sublimation so as to provide the substantially constant availability of the inhibitors. In other words, vapor phase corrosion inhibitors typically emit vapors which protect corrodible surfaces through the deposition or condensation of a protective film or coating upon the surface. In order to be assured that a constant supply of inhibitor be present, adequate quantities of the solid phase or liquid phase corrosion inhibiting compounds must be provided, with the corrosion inhibiting compounds being released at or adjacent the location where needed.
Granular silica gel is widely available for use as a desiccant. Frequently, granular silica gel is placed within a woven or knit pouch and placed within the confines of a package or enclosure for enveloping a corrosion-susceptible article. The granular material, when maintained at a particle size of below about 8 .mu.m may be utilized as a solid-phase substrate upon which powdered vapor phase corrosion inhibitor materials may be deposited.
When a laminate is formed in which one layer comprises a heat sealable film such as polyethylene with composite compositions of the present invention extruded in-situ, and with a second film layer being a material such as metallized stress-oriented polyethylene terephthalate films with desirable combinations of properties are achieved. Specifically, the polyethylene film layer retains its conventional heat sealing properties, while the stress-oriented polyethylene terephthalate provides a tear-resistant property. The metallized layer is utilized to reduce and/or eliminate static build-up, thereby further enhancing the properties and qualities of the laminate. Stress-oriented polyethylene terephthalate is normally biaxially oriented, and is, of course, commercially available. The composite vapor phase corrosion inhibiting/desiccant materials of the present invention enhance the protective qualities of films which incorporate or otherwise include the composite materials.